This application in general relates to a planetary drive system for use in a vehicle axle assembly. More particularly, the present invention discloses a planetary drive system which minimizes the amount of lateral space used for transferring drive between drive and driven shafts.
Vehicles often have full or part-time four wheel drive. In such vehicles, a drive transmission is connected to both the front and rear axle assemblies through a differential to drive the axles. Typically, the rear axle is constantly driven, while the front axle is either selectively or constantly driven. In full-time four wheel drives, both axles are constantly driven. The provision of a differential for transmitting drive to the front axle requires space in an area of the vehicle where space is already at a premium. It has been a major goal of vehicle manufacturers over the past several years to minimize the size and space of the vehicle. This premium on space is particularly an issue in the engine compartment, which is adjacent to the area where the front axle differential is typically located.
In a well-known type of vehicle, the engine extends longitudinally along a lateral center axis of the vehicle. The front axle differential case might ideally be placed along the center axis. This presents a problem, however, since it would require additional height for the vehicle in the engine compartment. The engine and differential would both occupy the same lateral and longitudinal space requiring the engine to be stacked vertically above the differential. Thus, prior art vehicles may have offset the differential case to one lateral side of the vehicle center axis such that it lies adjacent to, rather than underneath, the engine. This also lowers the center of gravity for the vehicle, which is another goal of the vehicle designer.
While this solution does result in a reduction of required vertical height in the engine compartment, it presents further problems to the suspension system of the vehicle. Typically, vehicle suspension systems have axle halves extending from each of the wheels to the differential case, and connected to a drive member by a constant velocity universal joint. This allows the axle halves to pivot and move angularly relative to the drive member to accommodate the surface over which the vehicle is being driven. These suspension systems work well, provided the axle half is of a sufficient length that a relatively large movement of the wheel is translated into relatively reduced angle movement in the constant velocity universal joint. That is, the axle half could be envisioned as pivoting about an imaginary point within the constant velocity universal joint. The other end of the axle half adjacent to the vehicle may move a discrete distance with the wheel. The amount of angular movement at the pivot point for a particular discrete movement of the opposite end of the axle half, is reduced proportional to the length of the axle half. The longer the axle half, the smaller the angular movement at the pivot point. In order to increase the life of the joint it is desirable to minimize that angular movement.
Problems arise when this type of suspension is utilized in combination with the offset differential case discussed above. Since the differential case is spaced towards one lateral end of the vehicle, the axle half on that lateral end of the vehicle is allowed a reduced lateral distance to achieve an adequate axle half length.
One prior art solution to this problem was the inclusion of the constant velocity universal joint into the differential case on the lateral side that the differential case was spaced towards, defined here as the offset lateral side. The prior art axle drive that utilized this solution included a bevel gear drive system. While this solution did increase the length of the offset axle half, it is desirable to further increase its length.
Further, in such axle drive systems, it may be desirable to disconnect one of the axle halves from the drive shaft in part-time four wheel drive vehicles. While there have been prior art solutions to this problem, those solutions have involved relatively complex arrangements, and are thus somewhat undesirable.
It is an object of the present invention to disclose a drive system for use with offset differential cases which increases the length of the axle half on the offset side. Further, it is an object of the present invention to disclose a relatively simple disconnect system for disconnecting one of the axle halves from its drive member when the front axle is not being driven.